The international career of Scott MacLeod is hanging in the balance for the second time after it was revealed that the Scotland lock has failed another drugs test.

An investigation has been launched by the Scottish Rugby Union following the shock news the Scarlets forward gave a urine sample containing abnormally high levels of testosterone.

Despite the 21-cap player's reported claims of innocence, he has been suspended from all training and matches for both club and country.

It is the second time MacLeod, 29, has been forced to fight to clear his name in less than a year after he failed another doping test in January.

On that occasion, a judicial committee accepted his claim his positive test had been caused by a recent change in asthma medicine.

Although it is the responsibility of the player to make sure they have the relevant Therapeutic Use Exemption for any illness or condition that requires them to take medication that is on the World Anti-Doping Agency's Prohibited List, MacLeod escaped a ban on that occasion.

"As part of Scottish Rugby's anti-doping regulations a process is now under way," the SRU said in a statement last night. "Until that due process is complete it would be inappropriate for us to make any further comment."

Stuart Gallacher, chief executive of MacLeod's Welsh region, called for the investigation to be carried out as quickly as possible.

He said in a statement: "The Scottish Rugby Union has informed us that a urine test sample provided by Scarlets player Scott MacLeod has shown an irregularity.

"As standard procedure, while this irregularity is being investigated further, Scott MacLeod will not be playing or training with the Scarlets until the matter has been resolved.

"The player and the Scarlets management, along with the Scottish Rugby Union, hope to conclude this matter as soon as possible.